1. Field of the Invention
The present invention relates to a noncontacting electrostatic recording apparatus for forming an electrostatic recording image without bringing a recording head and a recording medium into contact with each other.
2. Description of the Related Art
A multistylus printer is conventionally well known as an electrostatic recording apparatus. This multistylus printer has a recording head constituted by arranging a large number of needle-like electrodes (styluses) in a main scanning direction with equal small intervals therebetween and selectively applies a voltage to each needle-like electrode in accordance with a recording signal to directly perform discharging on paper, thereby forming an electrostatic latent image. In this printer, in order to easily and stably hold an electric charge on paper, specialty paper coated with a high electrical resistance agent is used. Specialty paper of this type, however, is difficult to write something on it with a pen or a pencil and has a problem in storage stability because it is denatured depending on environmental conditions such as a humidity. Therefore, this specialty paper is not preferred as office paper.
In addition, when a gap between the distal end of each needle-like electrode and the surface of paper is large, a discharge electric field from the needle-like electrodes is widened on the paper surface to increase the size of formed dots, thereby making it difficult to obtain a high-resolution recording image. Therefore, a gap material is provided on the paper surface and brought into slidable contact with the distal ends of the needle-like electrodes to ensure a small gap. However, this system has a problem in that the distal ends of the needle-like electrodes are abraded or wear down.
Therefore, as an electrostatic recording system capable of using plain paper and ensuring a small gap between an image medium and the distal ends of recording electrodes, there is a system for forming a toner image on a drum-like intermediate recording medium and transferring the toner image on paper. According to this system, since the size of an apparatus tends to be increased due to the use of an intermediate recording medium, a process of simultaneously performing recording and development is adopted to avoid the increase in apparatus size. In this case, a large number of recording electrodes extending in a conveying direction (sub scanning direction) of a developing agent convey path are aligned in its widthwise direction (main scanning direction), and a developing agent is selectively transferred from the recording electrodes to the surface of an opposite electrode also serving as an intermediate recording medium in accordance with dot recording information, thereby developing a toner recording image consisting of dots.
In the above system, however, if the length of each recording electrode extending in the sub scanning direction is about one dot, an electric field capable of transferring toner cannot be obtained to fail to increase the image density. Therefore, the recording electrode length must be five to ten times the dot pitch in the sub scanning direction. That is, a development region becomes five to ten times the dot pitch. Therefore, when continuous recording of two or more dots is performed, the toner adhesion amount becomes larger as the dot position becomes later. For example, since the second dot in two-dot continuous recording is formed by repeatedly performing development twice (superposition development), the adhesion amount of toner is about twice that of the first dot. In this manner, since the toner adhesion amount becomes larger as the dot position becomes later, a built-up toner aggregate is broken to enlarge the dot in a trailing end portion of a continuously recorded image, thereby degrading the reproducibility. That is, the contour of the trailing end portion of an image is enlarged to form a low-resolution recording image worse in so-called sharpness.
In addition, in the above system, since the intermediate recording medium is repeatedly used, the intermediate recording medium must be cleaned each time it is used so as not to produce any residual image. However, if a cleaning means is provided around the intermediate recording medium, the size of an electrostatic recording apparatus is increased.